Parkinson's HelpLine

Science News

Do Parkinson's drugs create obsessions?

Eight years ago, neurologist Mark Stacy encountered a strange problem with two of his patients.

Both men had Parkinson's disease, and they suddenly developed an out-of-control urge to gamble. Both maxed out their credit cards and lost $60,000 in just a few short months.

Stacy realized that the gambling sprees started just after he had increased each man's dose of a drug to control Parkinson's, a movement disorder that afflicts up to 1 million people in the USA.

Stacy wasn't ready to sign on to the idea that the medication could trigger a gambling habit. So he kept close track of his patients. By 2003, he had collected nine cases of pathological gambling that appeared to be tied to a class of drugs used to treat Parkinson's patients.

That report, published in the August 2003 issue of Neurology, and other reports around the same time suggested that the problem was rare.

Back then, Stacy and other experts couldn't prove the link between the drugs and the obsessive behavior. They still don't have hard-and-fast proof, but as the evidence accumulates, many scientists now say the drugs can kick off compulsive urges in certain people.

And they say the side effect is anything but rare.

At a meeting in Toronto last month, Stacy and other experts reviewed the cases reported so far and concluded that the drugs appear to trigger a syndrome of bad behavior that includes compulsive gambling, shopping, binge eating and an unstoppable urge for sex.

"Fifteen percent of all Parkinson's patients might have this syndrome," Stacy says. If he's right, that could mean as many as 150,000 people in the USA are struggling with out-of-control behavior. Even those numbers may underestimate the problem.

Stacy says many patients are ashamed to admit they have developed a gambling problem or an obsession with sex. And doctors can be skittish about talking about compulsive behaviors that are considered shameful, taboo or just plain odd.

The syndrome, dubbed impulse control disorder, is associated with a class of drugs known as dopamine agonists, says Melissa Nirenberg, a neurologist who has studied the disorder at the Weill Cornell Medical College in New York. The drugs control the tremors, shuffling and other symptoms of the disease. She says many patients develop irresistible urges after they get an increase in the medication.

And in some cases, the behavior stops on a dime after the dosage has been lowered, she says.

Nirenberg says she had one patient who gained 60 pounds after her medication was increased. She would get up and binge-eat late at night until finally her husband put a padlock on the refrigerator, she says.

Other examples of out-of-control behavior linked to the drugs include:

A man who stayed up all night obsessively taking his lawn mower apart and then putting it back together.

A shopaholic who ran up bills of $100,000 before the compulsion was linked to drugs for Parkinson's. This woman and many others paid a steep price for the side effect: Her marriage ended over the turmoil caused by the financial difficulties.

No one really knows how the drugs trigger the compulsions. One theory holds that the drugs seem to turn normal urges to have pleasurable activities such as sex or good food into an unstoppable craving. "It's a lot like an addiction," Stacy says.

Drugs such as Mirapex or Permax act on protein receptors in the brain that interact with a feel-good brain chemical called dopamine. Older drugs for Parkinson's actually increase the amount of dopamine in the brain. Stacy and other researchers believe the tweaking of the dopamine system somehow produces a reward or a pleasurable feeling whenever the patient acts on an urge.

At the same time, he says, the drugs may somehow turn off the part of the brain that controls risky behavior.

Some other scientists and the drug companies suggest that science has not been able to determine whether the drugs cause a compulsion.

Boehringer Ingelheim Pharmaceuticals, which makes Mirapex, has toughened its warning label to make sure doctors are aware of the reports linking the drug to such behaviors.

Kate O'Connor, a spokeswoman for Boehringer, says there's still just a collection of cases and no proof that drugs such as Mirapex cause the behaviors. "The evidence is not conclusive," she says.

To get proof, scientists will need bigger studies involving more people, says Wendy Galpern, a program officer at the National Institute of Neurological Disorders and Stroke. Still, she and others believe the evidence is strong enough to warn Parkinson's patients that the drugs have been linked to these behaviors. "It's important for people to be aware of these problems," she says.

The obsessions, even if seemingly harmless, such as a compulsion to collect odd items, can isolate patients, Stacy says, and there's no doubt that compulsive gambling or shopping can be destructive.

"These behaviors can destroy families," Nirenberg says. "People have lost all of their money, and they've damaged relationships."

She urges patients and family members to have a frank talk with the doctor, especially if they have noticed odd behavior.

Patients shouldn't be afraid to talk about gambling, overeating or a compulsion to shop.

"It's a side effect of the medication," she says. "I don't think the patients should be blamed."